step 4: add async tiles and persistent cache

tests/test_tiles.py

@@ -0,0 +1,87 @@
+from __future__ import annotations
+
+from io import BytesIO
+
+from PIL import Image
+
+from dpg_map.providers import OSM
+from dpg_map.tiles import (
+    TileID,
+    TileManager,
+    TileResult,
+    TileStatus,
+    calculate_visible_tiles,
+    decode_tile_image,
+)
+
+
+def test_visible_tile_calculation_uses_provider_namespace() -> None:
+    tiles = calculate_visible_tiles(
+        center=(0.0, 0.0),
+        zoom=2,
+        width=256,
+        height=256,
+        provider=OSM,
+        margin=0,
+    )
+
+    assert tiles
+    assert {tile.tile_id.provider_name for tile in tiles} == {"osm"}
+    assert all(0 <= tile.tile_id.x <= 3 for tile in tiles)
+    assert all(0 <= tile.tile_id.y <= 3 for tile in tiles)
+
+
+def test_tile_manager_ignores_stale_generation_results() -> None:
+    manager = TileManager()
+    stale = TileResult(
+        TileID("osm", 1, 0, 0),
+        generation=1,
+        status=TileStatus.READY,
+        width=1,
+        height=1,
+        pixels=(1.0, 1.0, 1.0, 1.0),
+        source="disk",
+    )
+    manager._result_queue.put(stale)
+
+    accepted = manager.drain_results(generation=2, provider_name="osm")
+
+    assert accepted == []
+    assert manager.snapshot().stale_results == 1
+
+
+def test_memory_eviction_protects_visible_tiles() -> None:
+    manager = TileManager(memory_cache_max_tiles=1)
+    protected = TileID("osm", 1, 0, 0)
+    evictable = TileID("osm", 1, 0, 1)
+    with manager._lock:
+        manager._visible_tile_ids = {protected}
+
+    for tile_id in (protected, evictable):
+        manager._result_queue.put(
+            TileResult(
+                tile_id,
+                generation=1,
+                status=TileStatus.READY,
+                width=1,
+                height=1,
+                pixels=(1.0, 1.0, 1.0, 1.0),
+                source="disk",
+            )
+        )
+
+    manager.drain_results(generation=1, provider_name="osm")
+
+    assert manager.get_ready_tile(protected) is not None
+    assert manager.get_ready_tile(evictable) is None
+
+
+def test_decode_png_tile_image() -> None:
+    image = Image.new("RGBA", (1, 1), (255, 0, 128, 255))
+    buffer = BytesIO()
+    image.save(buffer, format="PNG")
+
+    width, height, pixels = decode_tile_image(buffer.getvalue())
+
+    assert (width, height) == (1, 1)
+    assert pixels == (1.0, 0.0, 128 / 255, 1.0)